Key for building blocks



FIG. 1 is a perspective view of a key for building blocks according tothe design;

FIG. 2 is a side elevational view thereof;

FIG. 3 is an opposite side elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a front elevational view thereof; and,

FIG. 7 is a rear elevational view thereof.

The ornamental design for a key for building blocks, as shown.